Scientists study nesting patterns of threatened sea turtles in Gulf

Published: Saturday, July 20, 2013 at 6:01 a.m.

Last Modified: Saturday, July 20, 2013 at 11:18 p.m.

Scientists studying threatened loggerhead sea turtles in the northern Gulf of Mexico have found the turtles cover hundreds of miles from their nesting sites to feeding grounds offshore in a single season.

This migration takes them through waters impacted by the oil and fishing industries, and evidence from a new U.S. Geological Survey study suggests the turtles may require broader habitat to recover. The findings also cast new uncertainty on estimates of the turtles’ population size, which could be smaller.

“This is the first study to locate and quantify in-water habitat use by female loggerheads in the northern Gulf of Mexico subpopulation during their reproductive periods,” said lead author Kristen Hart, a U.S. Geological Survey research ecologist. “Our tracking results show they depend on a much broader range of habitat during this critical part of their lives than was previously thought to be required.”

The study challenged the widely held view that loggerhead sea turtles remain near one beach throughout their nesting season. It detailed loggerhead movements between nesting seasons, showing patterns that vary for individual turtles.

The period between nesting begins when females return to shore from the open Gulf around May and lasts until September. Efforts to protect these turtles generally targeted beaches with high nesting activity under the assumption that once turtles had nested on those beaches, they remained in the immediate area or migrated back to sea.

“The satellite data and our observations on the ground tell the same story: loggerheads in this subpopulation nest at multiple beaches, sometimes hundreds of miles apart,” Hart said. “Some of the females we captured and tagged on beaches in Alabama traveled over 250 miles to nest in Florida, where we recaptured them. Likewise, we also captured some females in Alabama that had previously been tagged at the Florida site in earlier breeding years.”

Researchers analyzed where 39 adult female sea turtles went after they nested on beaches in Alabama and Florida between 2010 and 2012 to learn where they spent time in the water during the breeding season before migrating back to sea.

Loggerhead sea turtles are found throughout the Gulf of Mexico and Atlantic coast, nesting in the U.S. from the coasts of Texas to Virginia.

“We were surprised to find a lot of variation in their behavior,” said Meg Lamont, study co-author and U.S. Geological Survey biologist.

On average, the tagged turtles visited areas about 20 miles from shore and moved about 17 miles to nest at another beach, she said. But some of them journeyed more than 124 miles to nest at additional beaches, while others simply cruised back out to sea after the first nesting.

The study results explain a mystery that had puzzled Lamont, who has 16 years of data from the St. Joseph Peninsula in Florida. It found that few of the nesting loggerheads they tagged returned to nest again in the same place.

“We didn’t know whether they were dying or simply nesting elsewhere,” Lamont said, “Now we know they aren’t as faithful to one nesting site as was once thought. The data shows it is not sufficient to just protect habitat around high density nesting beaches — such as the St. Joseph Peninsula — because many turtles that nest on the peninsula use the entire region from the eastern Florida Panhandle to Louisiana.”

There could also be fewer female loggerheads nesting in the northern Gulf than current estimates suggest because they are calculated using nest numbers.

“Our research shows that the same turtle could easily deposit eggs in Alabama and Florida if nests are separated by about two weeks,” Hart said. “Population numbers based on nest counts may therefore be biased upwards if nests at the two sites were assumed to have come from two different females.”

The study also noted that the areas the loggerheads visited between nests overlapped human activities such as shrimp trawling and oil and gas drilling.

Hart said scientists are working to define areas where sea turtles concentrate their activities at sea to create a map of Gulf of Mexico “turtle hotspots.”

“The more we know about their habitat use, the more questions are raised about their behavior and ability to adapt. We hope to build a better understanding of how frequently turtles return to these same locations and whether or not they move to new habitats when those locations are impacted, she said.

That can help scientists to develop better management strategies to help these endangered turtles recover.

<p>Scientists studying threatened loggerhead sea turtles in the northern Gulf of Mexico have found the turtles cover hundreds of miles from their nesting sites to feeding grounds offshore in a single season.</p><p>This migration takes them through waters impacted by the oil and fishing industries, and evidence from a new U.S. Geological Survey study suggests the turtles may require broader habitat to recover. The findings also cast new uncertainty on estimates of the turtles' population size, which could be smaller. </p><p>“This is the first study to locate and quantify in-water habitat use by female loggerheads in the northern Gulf of Mexico subpopulation during their reproductive periods,” said lead author Kristen Hart, a U.S. Geological Survey research ecologist. “Our tracking results show they depend on a much broader range of habitat during this critical part of their lives than was previously thought to be required.”</p><p>The study challenged the widely held view that loggerhead sea turtles remain near one beach throughout their nesting season. It detailed loggerhead movements between nesting seasons, showing patterns that vary for individual turtles. </p><p>The period between nesting begins when females return to shore from the open Gulf around May and lasts until September. Efforts to protect these turtles generally targeted beaches with high nesting activity under the assumption that once turtles had nested on those beaches, they remained in the immediate area or migrated back to sea.</p><p>“The satellite data and our observations on the ground tell the same story: loggerheads in this subpopulation nest at multiple beaches, sometimes hundreds of miles apart,” Hart said. “Some of the females we captured and tagged on beaches in Alabama traveled over 250 miles to nest in Florida, where we recaptured them. Likewise, we also captured some females in Alabama that had previously been tagged at the Florida site in earlier breeding years.” </p><p>Researchers analyzed where 39 adult female sea turtles went after they nested on beaches in Alabama and Florida between 2010 and 2012 to learn where they spent time in the water during the breeding season before migrating back to sea. </p><p>Loggerhead sea turtles are found throughout the Gulf of Mexico and Atlantic coast, nesting in the U.S. from the coasts of Texas to Virginia.</p><p>“We were surprised to find a lot of variation in their behavior,” said Meg Lamont, study co-author and U.S. Geological Survey biologist. </p><p>On average, the tagged turtles visited areas about 20 miles from shore and moved about 17 miles to nest at another beach, she said. But some of them journeyed more than 124 miles to nest at additional beaches, while others simply cruised back out to sea after the first nesting.</p><p>The study results explain a mystery that had puzzled Lamont, who has 16 years of data from the St. Joseph Peninsula in Florida. It found that few of the nesting loggerheads they tagged returned to nest again in the same place. </p><p>“We didn't know whether they were dying or simply nesting elsewhere,” Lamont said, “Now we know they aren't as faithful to one nesting site as was once thought. The data shows it is not sufficient to just protect habitat around high density nesting beaches — such as the St. Joseph Peninsula — because many turtles that nest on the peninsula use the entire region from the eastern Florida Panhandle to Louisiana.”</p><p>There could also be fewer female loggerheads nesting in the northern Gulf than current estimates suggest because they are calculated using nest numbers. </p><p>“Our research shows that the same turtle could easily deposit eggs in Alabama and Florida if nests are separated by about two weeks,” Hart said. “Population numbers based on nest counts may therefore be biased upwards if nests at the two sites were assumed to have come from two different females.” </p><p>The study also noted that the areas the loggerheads visited between nests overlapped human activities such as shrimp trawling and oil and gas drilling.</p><p>Hart said scientists are working to define areas where sea turtles concentrate their activities at sea to create a map of Gulf of Mexico “turtle hotspots.”</p><p>“The more we know about their habitat use, the more questions are raised about their behavior and ability to adapt. We hope to build a better understanding of how frequently turtles return to these same locations and whether or not they move to new habitats when those locations are impacted, she said.</p><p>That can help scientists to develop better management strategies to help these endangered turtles recover.</p>